1. Field of the Invention
The present invention relates to a particle implantation apparatus and a particle implantation method for uniformly implanting a large amount of particles having low energy into a substrate by the sputtering method.
2. Description of the Related Art
In recent years, in a semiconductor device manufacturing field, there is a demand for a technique for uniformly implanting a large amount of particles having low energy into the substrate. For example, in manufacturing the semiconductor devices such as a field effect transistor (e.g., MOS-FET) by implanting impurities in the form of ions into the semiconductor substrate, implantation area becomes shallow as the scale of integration of such devices increases in recent years. Therefore, it is required to implant impurities having lower energy than before (e.g., in a range from several eV to hundreds eV, several keV at most).
However, if ions (ion beam) having low energy are extracted from an ion source, an ion beam current that can be extracted suddenly decreases, because the ion beam current decreases in proportion to the 3/2-th power of an extraction voltage (called a 3/2-th power proportion rule). In this case, it is difficult to implant a large amount of ions, so that the implantation treatment capability (through-put) abruptly decreases.
At present, a technique is employed in which an ion beam extracted from the ion source at fully higher energy than several keV is decelerated by a decelerator and transported at low energy of interest below several keV for implantation. However, in a case of transporting the ion beam having low energy below several keV, the ion beam is greatly diverged due to its space charge effect, resulting in an extremely low transport efficiency of the ion beam, especially when the ion beam having a low energy and a large current is transported. This is because when the ion beam has a large current, its space charge effect is large, and when the ion beam has a low energy, the ion beam is easily affected by the divergence due to space charge. Accordingly, with the above technique, it is difficult to implant a large amount of ions having low energy into the substrate.
It is an object of the present invention to provide a particle implantation apparatus and a particle implantation method that can uniformly implant a large amount of particles having low energy into the substrate.
In order to accomplish the objective above, the following means are adopted. According to the present invention, there is provided an apparatus for implanting particles onto a substrate comprising:
a target for sputtering;
an ion beam source for applying an ion beam apparently like a sheet wider in a X direction onto the target so as to generate sputter particles from the target by the sputtering;
a target scanning mechanism for mechanically scanning the target in a Y direction crossing the X direction in reciprocating manner at a fixed angle with respect to the ion beam;
a slit plate having a long slit extending in the X direction for passing the sputter particles generated from the target;
a holder for holding the substrate at a position where sputter particles having passed through the slit of the slit plate are incident; and
a holder scanning mechanism for mechanically scanning the holder in a Z direction crossing both the X and Y directions in reciprocating manner.
The ion beam source generates the ion beam apparently like a sheet by scanning a spot-like ion beam electrically or magnetically in reciprocating manner, or may generate the ion beam actually like a sheet without scanning.
Since this particle implantation apparatus implants the ion beam from the ion beam source not to the substrate but to the target, the ion beam applied to the target may have a higher energy than several keV. If the ion beam having high energy is employed, it is possible to avoid the problems with an ion beam current reduction according to the 3/2-th power proportion rule and a lower transport efficiency due to space charge. Therefore, the ion beam can be applied by large amount (in large current) to the target. Further, the energy range of high sputtering rate can be utilized. As a result, a large amount of sputter particles can be produced by sputtering from the target. The xe2x80x9csputter particlesxe2x80x9d means particles flown out from the target by sputtering.
Though sputter particles produced by sputtering are composed of neutral particles and positive ions and etc., it is empirically known that the energy of sputter particles is distributed over a range from several eV to about 20 eV, irrespective of the energy of applied ion beam. With the above configuration, a large amount of sputter particles having low energy can be implanted into the substrate. Accordingly, the implantation treatment capability at low energy is enhanced.
Incidentally, in a well-known sputtering apparatus, two dimensional large area ion beam covering an almost entire area of a target is applied to the target, and sputter particles produced from the target are made incident directly on the substrate (e.g., refer to JP-A-4-314860).
On the contrary, in the present invention, the ion beam apparently like a sheet wider in the X direction can be applied from the ion beam source to the target, in which it is only necessary for the ion beam to be uniform in the X direction alone. Hence, the ion beam can be applied more uniformly than the two dimensional large area ion beam with a density distribution like a mountain which is usually dense in the central portion and sparse in the peripheral portion. In particular, the ion beam is easily scanned in the X direction. Accordingly, sputter particles are produced uniformly in the X direction from the target. Hence, the sputter particles can have more uniform density distribution and more aligned angle of incidence for sputter particles incident on the substrate than the sputter particles produced by applying the two dimensional large area ion beam. Since the holder scanning mechanism allows the substrate on the holder to be scanned in the Z direction crossing the X direction, and the sputter particles are produced uniformly in the X direction, the sputter particles can be uniformly incident on a wide area (e.g., almost entire area) of the substrate and uniformly implanted into the wide area of the substrate. Furthermore, a great number of sputter particles having low energy can be implanted as previously described.
Moreover, in the present invention, since sputter particles can be incident on the substrate through the slit extending long in the X direction of the slit plate, the angles of incidence for the sputter particles incident on the substrate can be aligned. Accordingly, the implantation characteristic can be enhanced.
Further, in the present invention, the target scanning mechanism is provided to mechanically scan the target in the Y direction, whereby a wide area of the target is utilized for sputtering. If the target is fixed, and the sputtering is made at the same location continuously, the target is locally cut to change the sputtering situations including the direction and amount of discharged sputter particles, whereby it is difficult to make the sputter particles uniformly incident on the substrate and uniformly implanted in a short time. However, this problem can be resolved by the scanning of the target. Accordingly, from this point of view, the implantation treatment capability at low energy can be also enhanced.
The particle implantation apparatus may further comprise an acceleration power source for applying a DC accelerating voltage having a positive target side between the target and the holder. In this manner, because positive ions contained in the sputter particles produced from the target are accelerated by the accelerating voltage and implanted into the substrate, it is possible to realize implantation (ion implantation) in a higher energy range than the intrinsic energy (several eV to about 20 eV as previously mentioned) of sputter particles.
The particle implantation apparatus may further comprise an energy filter between the target and the holder for selectively deriving positive ions having a specific energy. In this manner, the energy of positive ions implanted into the substrate is limited to a specific value. It is possible to prevent neutral particles in the sputter particles or the incident ions repelled against the target from being incident on the substrate. As a result, it is possible to realize the precise particle implantation (ion implantation) with the desired energy of implantation ions.